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ULN2803 Tester


John_W._Couvillon
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Hi John,

I am wondering why you are talking about using the ULN2803 chip with the matrix board. It combines the Din and Dout functions which use shift registers 74HC165 and 74HC595. The schematic is shown here. http://www.ucapps.de/mbhp/mbhp_dio_matrix.pdf On the Dout board you can substitute the ULN2803 chips for the resistor packs if you want to drive larger loads. This can not be done on the DIO-MATRIX board.

 

Update: Now that I posted this I wonder if you are talking about another Matrix PCB that I don't know about.

 

Pete

Edited by kpete
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ULN2803 is a a chip containing darlington transistors, which can be used with a broad output voltage (depends what u feed it with). It also got protection diodes at each output, so, all this makes is extremely usefull as interface between shift registers / i/o pins of microcontroller and relays.

 

So I guess, the question kpete asks, is a valid questions. Would be easier to tell you what might be wrong if you provided a schem, or told a little more about the matrix and what u're trying to use the 2803 chips for. Not sure what you're building and what you ask for, but in general, if any circuit need a new IC each time you use it, something is definetly wrong with it :).

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Pete, Technobreath;

yes you are correct, however I have added several DOUTs to the two matix pcbs that are feed by my LPC17. the ULN2803's feed the magnets on 32 SAMS and  overheat for no apparent , obvious ,reason.  Now i have a pile of ULN's and don't know if they are good or bad.  I hesitate to plug a questionable chip into a working circuit.  Yes the ULN's are cheap, but just the same.

Thanks

Johnc

Edited by John_W._Couvillon
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So, it's not a case of the magnets acting like coils? Do you have a coil spike suppression diode connected? Just thinking out loud here. There might be a bit of an inductive kick. Or, is there a short or current rush at some point of the switching pulse? Take this for what it is, I'm just leery of anything coil like. /J

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Ah-haaaa, more information is what was needed.

 

As Technobreath states, you MUST have the kick-back diodes on the 2803 connected to your SAM's common rail of +12v. This is pin 10 on the 2803.

 

To check out your ULN2803's, just pull the shift registers out of the sockets of the DOUT board and apply the +12v to the SAM's. With the inputs open, none of them should be turned on. With 12v on, take a volt meter and measure the voltage on pins 1 thru 8 of the 2803. They should all read 0 volts. Now take a wire from +5 volts and touch it to the input of each of the darlington drivers. These are pins 1 thru 8 on the IC. You should see each of the SAM's toggle ON and OFF. Note:Make sure that you have Pins 11 thru 18 going to the SAM magnets. If they aren't, you will blow up your core board by applying 12v to the 5v rail.

 

Another issue might be where you think pin 1 is for the 2803 chip on the DOUT board. Pins 1 thru 8 on the 2803 chip should be going to the shift registers.

 

The 3rd issue is the currents you are pulling thru the DOUT board. You will have to add more ground wires to the already existing DOUT board and tie these to the ground of your hefty 12v power supply ground. Each SAM magnet will pull 500ma thru the 2803 chip. These currents might interfere with the digital signals going to the shift registers if your not careful. Ground loops thru the 10 pin ribbon cable may be another issue. You want to make sure that you only turn ON a max of 4 drivers for no more than 250ms. 80-100ms should be enough to get the SAM to switch states.

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